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Dec 1989

Volume 60, Issue 12, pp. 3597-3835

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Ultrashort light pulses

John D. Simon

Rev. Sci. Instrum. 60, 3597 (1989); http://dx.doi.org/10.1063/1.1140516 (28 pages) | Cited 12 times

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This article reviews the generation and amplification of ultrashort laser light pulses, τp≤10−12 s. Current methods for generating optical pulses in the ultraviolet, visible, and infrared regions of the spectrum are described. Devices based on mode‐locking techniques, as well as various novel sources for ultrashort light pulses, are examined. In addition, recent advances in using fiber optics to shape and compress optical pulses are presented. Optical amplifiers that have been developed to generate kilowatt and higher peak powers at a variety of repetition rates are described and compared. In the last section of the paper, various nonlinear optical techniques that have been developed to extend the tuning range of ultrashort laser pulses are briefly discussed.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking

Performance of an automated rotating‐detector ellipsometer

David C. Nick and R. M. A. Azzam

Rev. Sci. Instrum. 60, 3625 (1989); http://dx.doi.org/10.1063/1.1140517 (8 pages) | Cited 3 times

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A computer‐controlled rotating‐detector ellipsometer (RODE) has been constructed using a windowless planar‐diffused Si photodiode, a stepping motor, an operational amplifier, and a personal computer (PC) equipped with an A/D‐D/A converter. The detector is mounted to the output shaft of the stepping motor at an optimum angle of incidence of ∼59° and is rotated through 360° about the incident beam as an axis. The detector output signal voltage is measured and stored in the PC at every 2° increment of the RODE angle θ. Fourier analysis of the recorded data provides a handedness‐blind determination of the state of polarization of the incident light. A beam from a HeNe laser (λ=632.8 nm) is transmitted through the polarizing optics of an ellipsometer to provide the polarization states needed for calibration and testing. The calibration parameters mL and θr are determined by rotating the detector about a linearly polarized beam of light of zero reference azimuth. The RODE is subsequently tested and found to correctly measure the first two normalized Stokes parameters of a number of states with a residual rms error of ∼0.002. This limit on precision is dictated mainly by the 12‐bit A/D converter. A small angular misalignment of the rotation axis of the detector with respect to the light‐beam axis introduces odd harmonics in the detector signal; hence, its effect is readily isolated by appropriate data reduction. Thin‐film coatings on the detector surface that significantly improve the performance of the RODE are proposed.
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07.60.Fs Polarimeters and ellipsometers

New polarization‐modulation spectrometer for simultaneous circular dichroism and optical rotatory dispersion measurements. II. Design, analysis, and evaluation of a prototype model

Yohji Shindo, Kazuko Mizuno, Masahiro Sudani, Hiroshi Hayakawa, Yasuhiro Ohmi, Nobuyuki Sakayanagi, and Norimasa Takeuchi

Rev. Sci. Instrum. 60, 3633 (1989); http://dx.doi.org/10.1063/1.1140467 (7 pages) | Cited 5 times

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We have designed and constructed a prototype model of a new polarization‐modulation spectrometer for simultaneous circular dichroism (CD) and optical rotary dispersion (ORD) measurements based on the results of our preliminary experiments. The Mueller matrix approach is used to analyze and evaluate important factors determining the performance of our new spectrometer. The CD and ORD base‐line shifts are found to be an indicator representing the total performance of the spectrometer. The capability of our spectrometer in measuring CD and ORD signals is equal to that of commercially available CD and ORD spectropolarimeters in the wavelength range from 220 to 700 nm. Furthermore, our spectrometer has much faster speed of ORD measurement than the ORD spectropolarimeter of null‐point detection type. Our spectrometer has also high sensitivity to both linear birefringence and linear dichroism measurements.
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07.60.Rd Visible and ultraviolet spectrometers

Enhanced dc arc lamp performance for spectroscopic applications

Randall L. Woodlee, Ming‐Ren S. Fuh, Gabor Patonay, and Isiah M. Warner

Rev. Sci. Instrum. 60, 3640 (1989); http://dx.doi.org/10.1063/1.1140468 (3 pages) | Cited 1 time

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The performance of a high‐pressure xenon arc lamp is enhanced by application of a combination of two techniques which (1) reduces noise due to arc wander and (2) increases the lamp intensity. Fluctuations in lamp intensity due to arc wander are minimized by the superimposition of an alternating current (ac) on the direct‐current (dc) source voltage in conjunction with detector averaging. Lamp intensity is increased by the application of a static magnetic field to the arc plasma. Arc stability and intensity are monitored indirectly by measuring arc‐excited Rhodamine B fluorescence. Data illustrating the effects of each technique individually and in combination are presented. Lamp output is typically maintained to less than 1% relative standard deviation while intensity is increased by as much as 127%.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Yr Discharges for spectral sources (including inductively coupled plasma)
07.60.Rd Visible and ultraviolet spectrometers

Measurement of the absolute spectral response of an inverse photoemission detector

Recep Avci, Qing Cai, and Gerald J. Lapeyre

Rev. Sci. Instrum. 60, 3643 (1989); http://dx.doi.org/10.1063/1.1140469 (4 pages) | Cited 12 times

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The absolute quantum yield of an inverse photoemission detector is reported. The detector consists of a 650‐Å KBr photoemission film on the mouth of a channeltron with either a CaF2 or a SrF2 window for a low‐pass cutoff filter. The spectral response for the CaF2 window peaks at 9.8 eV with a FWHM of 1.6 eV and a maximum yield of 0.18 pulse/photon, while for the SrF2 window the peak is at 9.3 eV with a FWHM of 1.4 eV and a maximal yield of 0.06 pulse/photon. Performance of the detector was tested by measuring the inverse photoemission spectra from a W(001)‐(1×1) surface.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.90.+c Other topics in instruments, apparatus, and components common to several branches of physics and astronomy (restricted to new topics in section 07)

Apparatus and experimental procedures for surface electron spectroscopies using incident ions, metastable atoms, and photons

E. E. Chaban, H. D. Hagstrum, and P. Petrie

Rev. Sci. Instrum. 60, 3647 (1989); http://dx.doi.org/10.1063/1.1140470 (9 pages) | Cited 1 time

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Two major additions to our multiexperiment apparatus are presented in this article. They are a metastable beam apparatus which produces 108 metastables per s and a sample manipulator that provides cooling of the sample to liquid‐nitrogen temperature and flash heating to 1500 K following by rapid return to LN temperature. We also present new versions of our ion beam and photon beam apparatus. The ion beam source produces a 5×10−10A, focussed beam of noble gas ions at kinetic energies less than 10 eV. We discuss features of a K+ ion source, a Te evaporator, and our method of data presentation.
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73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
79.60.-i Photoemission and photoelectron spectra

Apparatus for positron annihilation‐induced Auger electron spectroscopy

Chun Lei, David Mehl, A. R. Koymen, Fred Gotwald, M. Jibaly, and Alex Weiss

Rev. Sci. Instrum. 60, 3656 (1989); http://dx.doi.org/10.1063/1.1140471 (5 pages) | Cited 23 times

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The apparatus used in the first direct measurement of energy spectra of positron annihilation‐induced Auger electrons is described. The apparatus consists of a magnetically guided low‐energy positron beam, a UHV surface preparation and characterization chamber, and an energy spectrometer. The spectrometer includes a trochoidal monochromator and a microchannel plate detector. A permanent magnet is mounted behind the sample to produce a field gradient which redirects the outgoing Auger electrons along the spectrometer axis. The combination of trochoidal monochromator and permanent magnet permits the measurement of the total kinetic energy of Auger electrons with an effective angular acceptance of ∼2π. The large angular acceptance and single particle detection capability of this spectrometer make it possible to perform Auger measurements using extremely low incident beam currents (∼10−15 A), and may make it useful in other low signal experiments. The spectrometer response function is modeled and compared to experimental results for different values of the magnetic field gradient.
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82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
29.40.Mc Scintillation detectors
29.25.Bx Electron sources

A new method for measuring absolute total electron‐impact cross sections with forward scattering corrections

Ce Ma, Phillip B. Liescheski, and R. A. Bonham

Rev. Sci. Instrum. 60, 3661 (1989); http://dx.doi.org/10.1063/1.1140472 (12 pages) | Cited 11 times

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In this article we describe an experimental technique to measure the total electron‐impact cross section by measurement of the attenuation of an electron beam passing through a gas at constant pressure with the unwanted forward scattering contribution removed. The technique is based on the different spatial propagation properties of scattered and unscattered electrons. The correction is accomplished by measuring the electron beam attenuation dependence on both the target gas pressure (number density) and transmission length. Two extended forms of the Beer–Lambert law which approximately include the contributions for forward scattering and for forward scattering plus multiple scattering from the gas outside the electron beam were developed. It is argued that the dependence of the forward scattering on the path length through the gas is approximately independent of the model used to describe it. The proposed methods were used to determine the total cross section and forward scattering contribution from argon (Ar) with 300‐eV electrons. Our results are compared with those in the literature and the predictions of theory and experiment for the forward scattering and multiple scattering contributions. In addition, Monte Carlo simulations were performed as a further test of the method.
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34.80.Bm Elastic scattering

Spatial charge cloud distribution of microchannel plates

Michael L. Edgar, Robert Kessel, Jonathan S. Lapington, and David M. Walton

Rev. Sci. Instrum. 60, 3673 (1989); http://dx.doi.org/10.1063/1.1140473 (8 pages) | Cited 18 times

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We describe an experiment to measure the spatial charge distribution produced by a microchannel plate intensifier with a new type of charge division readout, the ‘‘split strip’’ anode. This anode is a modified strip and strip anode which determines both the amount of charge deposited on each half of the anode and the centroid position for each event. We present experimental measurements of microchannel plate charge cloud distributions for a variety of detector operating conditions. We find that, as a first‐order approximation, one can assume the charge cloud to be azimuthally symmetric. Additionally, the charge cloud remains virtually unchanged from event to event and pore to pore. The general form of the radial distribution is best described by the sum of two exponential components whose scale and relative weights vary with detector operating conditions. The central component of the distribution is three to six times smaller than the outer, or ‘‘wing’’ component. Typically most of the charge is in the central component. We have determined the scale and relative weights of the two exponentials for a fixed microchannel plate/anode gap of 6.2 mm and a range of detector operating conditions. The most significant variable determining the charge cloud distribution is the voltage between the back of the microchannel plates and the anode. As this voltage is increased from 50 to 800 V, the scale length of the central component shrinks from 1.4 to 0.5 mm and the weight increases from 50% to 85%.
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42.79.Ls Scanners, image intensifiers, and image converters
42.79.Pw Imaging detectors and sensors
85.60.Gz Photodetectors (including infrared and CCD detectors)

A high magnetic field EPR spectrometer

F. Muller, M. A. Hopkins, N. Coron, M. Grynberg, L. C. Brunel, and G. Martinez

Rev. Sci. Instrum. 60, 3681 (1989); http://dx.doi.org/10.1063/1.1140474 (4 pages) | Cited 74 times

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We describe a tunable electron paramagnetic resonance (EPR) spectrometer designed to operate at frequencies between 160 and 525 GHz and magnetic fields of up to 20 T. To operate in such a broad frequency range we use a very stable optically pumped far infrared laser. The performance of the spectrometer has been measured with solid and liquid samples. This allows us to outline the potential uses of the spectrometer.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
76.30.-v Electron paramagnetic resonance and relaxation

A new high‐pressure cell for differential pressure‐jump experiments using optical detection

Jürgen Quednau and Gerhard M. Schneider

Rev. Sci. Instrum. 60, 3685 (1989); http://dx.doi.org/10.1063/1.1140475 (3 pages) | Cited 6 times

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A differential pressure‐jump autoclave with optical detection is described, which is capable of performing pressure jumps of about 150‐bar amplitude to either lower or higher pressures within the absolute pressure range up to 2.5 kbar. The principle of a rupture diaphragm is applied and the mechanical relaxation time of the apparatus is about 0.1 ms. Optical detection either of transmitted light or scattered light under an angle of 90° can be utilized to follow the progress of a chemical reaction. A test of appliction is given for the reaction of Ni with Murexide in aqueous solution.
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07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells
42.79.-e Optical elements, devices, and systems

Measurement of hypersonic velocities resulting from the laser‐induced breakdown of aerosols using an excimer laser imaging system

S. A. Schaub, D. R. Alexander, D. E. Poulain, and J. P. Barton

Rev. Sci. Instrum. 60, 3688 (1989); http://dx.doi.org/10.1063/1.1141074 (4 pages) | Cited 2 times

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In this article we describe a dual‐pulse excimer‐laser‐based imaging system used in the determination of ejected material velocities resulting from the interaction of KrF laser radiation (λ=248 nm, pulse width FWHM=17 ns, I≊1011 W/cm2) with 20‐μm aluminum particles under vacuum (P=10−5 Torr) conditions. Material velocities measured 200–400 ns after arrival of the incident pulse ranged from 450 to 1200 m/s.
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06.30.Gv Velocity, acceleration, and rotation
82.70.Rr Aerosols and foams
42.30.Va Image forming and processing

Microvelocity sensor for instantaneous velocity determination

R. H. Zee, B. Z. Jang, A. Mount, and C. J. Wang

Rev. Sci. Instrum. 60, 3692 (1989); http://dx.doi.org/10.1063/1.1140476 (6 pages) | Cited 3 times

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A new microvelocity sensor unit was developed to measure the instantaneous velocity of a high velocity impactor during the penetration process. The concept of this device is based on the induced current generated in a coil due to the passage of a magnet. A special digital circuit was designed to yield a spatial resolution of better than 0.05 in. by eliminating the problem of signal overlap. The precise time delays obtained from these signals can be used to determine the slowing down or energy loss of a high‐velocity projectile. The details of this sensor unit will be described and its resolution will be demonstrated. A light gas gun was used to propel aluminum projectiles to velocities up to 320 m/s. Energy loss of these high‐velocity projectiles in composites reinforced with polyethylene, polyester, and graphite fabrics as well as pure Kevlar fabric was measured using this system. Results show that this microvelocity sensor is capable of identifying various energy‐loss processes during the impact of high‐velocity projectiles.
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06.30.Gv Velocity, acceleration, and rotation
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Phase shift moire apparatus for automatic 3D surface measurement

J. J. J. Dirckx and W. F. Decraemer

Rev. Sci. Instrum. 60, 3698 (1989); http://dx.doi.org/10.1063/1.1140477 (4 pages) | Cited 10 times

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An instrument for automatic reconstruction of the surface of three‐dimensional objects is described. The apparatus is based on phase‐shifted shadow moire, a noncontacting optical metrological technique which we substantially improved by a new way of introducing the phase shift. The article includes details of construction and the ideas guiding the choice of component characteristics. Some typical measuring results are presented.
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07.90.+c Other topics in instruments, apparatus, and components common to several branches of physics and astronomy (restricted to new topics in section 07)
42.79.-e Optical elements, devices, and systems

Surface thermometry by laser‐induced fluorescence

L. P. Goss, A. A. Smith, and M. E. Post

Rev. Sci. Instrum. 60, 3702 (1989); http://dx.doi.org/10.1063/1.1140478 (5 pages) | Cited 36 times

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A novel laser‐induced fluorescence technique has been developed for measuring the surface temperature of reacting and nonreacting materials. The technique involves seeding the material to be examined with a temperature‐sensitive phosphor (Dy:YAG) and monitoring the laser‐induced fluorescence of the phosphor to determine the temperature. The Dy:YAG phosphor displays a temperature sensitivity in the range 300–1700 K. The technique has been applied to both reacting and nonreacting surfaces under laser excitation, allowing temperature and temporal‐history profiles to be determined.
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07.20.Ka High-temperature instrumentation; pyrometers
68.35.Md Surface thermodynamics, surface energies

A fast UV/visible pyrometer for shock temperature measurements to 20 000 K

H. B. Radousky and A. C. Mitchell

Rev. Sci. Instrum. 60, 3707 (1989); http://dx.doi.org/10.1063/1.1140479 (4 pages) | Cited 18 times

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An ultraviolet/visible pyrometer is described which can measure shock temperatures from 3000 to 20 000 K. The system is modular, and in general consists of six photomultiplier tubes and two linear intensified diode array/spectrograph systems which can cover the range from 250 to 800 nm. Extension of the pyrometer’s capabilities into the ultraviolet is necessary for accurate measurements above 8000 K. The nature of the shock environment requires the photomultiplier tubes to have rise times on the order of 2 ns, with a typical experiment lasting between 20 and 500 ns. The system measures absolute intensity, and is calibrated against a known tungsten lamp prior to each experiment. The highest temperature measured was 18 300 K for fluid Xe. The targets needed to contain this type of cryogenic sample are described as well.
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07.20.Ka High-temperature instrumentation; pyrometers
07.60.-j Optical instruments and equipment

A sensitive time‐resolved radiation pyrometer for shock‐temperature measurements above 1500 K

Mark B. Boslough and Thomas J. Ahrens

Rev. Sci. Instrum. 60, 3711 (1989); http://dx.doi.org/10.1063/1.1140480 (6 pages) | Cited 18 times

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An optical system has been developed which can determine time‐resolved temperatures in shocked materials by measuring the spectral radiance of light emitted from shocked solid samples in the visible and near‐infrared wavelength range (0.5–1.0 μm). It can measure temperatures as low as 1500 K and has been successfully used to observe shock‐induced chemical reactions in powder samples. The high sensitivity of this radiation pyrometer can be attributed to the large angular aperture (0.06 sr), the large bandwidth per channel (up to 0.1 μm), the large photodiode detection areas (1.0 cm2 ), and the small number of calibrated channels (4) among which light is divided. Improved calibration techniques, as well as the layout of the instrument, eliminate certain sources of error encountered in previous shock‐temperature experiments. Errors in the measured spectral radiance were reduced by: (1) recalibration before every experiment to account for changes in optical components; (2) direct calibration of voltage recorded at each digitizer to prevent transfer error by an intermediate step; (3) use of a spectral irradiance calibration lamp to exclude errors due to spatial inhomogeneities associated with spectral radiance sources; and (4) obtaining a large spatial average of light at each wavelength from the same portion of the sample to eliminate errors from possible inhomogeneities in the sample. The magnitude each of these errors could previously contribute was 1%–2% of the total signal. Absolute temperature uncertainties, determined from the standard deviation of the measured spectral radiances from the least‐squares‐fit values, are typically about 5%. Emissivities are poorly constrained by spectral radiance data because of a weak functional dependence, and uncertainties can easily exceed 50% for temperatures of around 2000 K.
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07.20.Ka High-temperature instrumentation; pyrometers
07.60.-j Optical instruments and equipment

A new method for in situ dynamic calibration of temperature sensors

R. Budwig and C. Quijano

Rev. Sci. Instrum. 60, 3717 (1989); http://dx.doi.org/10.1063/1.1140481 (4 pages)

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A new method for in situ dynamic calibration of temperature sensors has been developed. The method is nonintrusive and can be used on a variety of sensors mounted in a variety of configurations. Chopped laser heating is used to generate a step change in sensor temperature so that dynamic calibration may be accomplished. Results on the dynamic response of a thermistor in air flow are presented as an application. A procedure for estimating time constants using data from existing heat transfer correlations has also been described.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.20.Dt Thermometers

Temporal behavior of neutral particle fluxes in TFTR neutral beam injectors

J. H. Kamperschroer, G. M. Gammel, A. L. Roquemore, L. R. Grisham, H. W. Kugel, S. S. Medley, T. E. O’Connor, T. N. Stevenson, A. von Halle, and M. D. Williams

Rev. Sci. Instrum. 60, 3721 (1989); http://dx.doi.org/10.1063/1.1140482 (9 pages)

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Data from an E∥B charge exchange neutral analyzer (CENA), which views down the axis of a neutral beamline through an aperture in the target chamber calorimeter of the TFTR neutral beam test facility, exhibit two curious effects. First, there is a turn‐on transient lasting tens of milliseconds having a magnitude up to three times that of the steady state level. Second, there is a 720 Hz, up to 20% peak‐to‐peak fluctuation persisting the entire pulse duration. The turn‐on transient occurs as the neutralizer/ion source system reaches a new pressure equilibrium following the effective ion source gas throughput reduction by particle removal as ion beam. Widths of the transient are a function of the gas throughput into the ion source, decreasing as the gas supply rate is reduced. Heating of the neutralizer gas by the beam is assumed responsible, with gas temperature increasing as gas supply rate is decreased. At low gas supply rates, the transient is primarily due to dynamic changes in the neutralizer line density and/or beam species composition. Light emission from the drift duct corroborate the CENA data. At high gas supply rates, dynamic changes in component divergence and/or spatial profiles of the source plasma are necessary to explain the observations. The 720 Hz fluctuation is attributed to a 3% peak‐to‐peak ripple of 720 Hz on the arc power supply amplified by the quadratic relationship between beam divergence and beam current. Tight collimation by CENA apertures cause it to accept a very small part of the ion source’s velocity space, producing a signal linearly proportional to beam divergence. Estimated fluctuations in the peak power density delivered to the plasma under these conditions are a modest 3%–8% peak to peak. The effects of both phenomena on the injected neutral beam can be ameliorated by careful operation of the ion sources.
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52.75.-d Plasma devices
52.50.Gj Plasma heating by particle beams
52.55.Fa Tokamaks, spherical tokamaks

Extracted beam composition with a mixed isotope feed to a neutral‐beam system

L. R. Grisham, H. D. Falter, R. Hemsworth, and G. Deschamps

Rev. Sci. Instrum. 60, 3730 (1989); http://dx.doi.org/10.1063/1.1140483 (4 pages) | Cited 2 times

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Both the Tokamak Fusion Test Reactor and the Joint European Torus, two large magnetic confinement fusion devices, will use high‐powered tritium beams. The suggestion has been made that tritium consumption could be reduced if tritium is only fed into the plasma source and deuterium or hydrogen is used as the neutralization target by operating with deuterium or hydrogen fed independently into the neutralizer. We report on measurements we performed with deuterium and hydrogen, and of the beam contamination that occurs in such an operating mode.
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52.55.Fa Tokamaks, spherical tokamaks

Multichannel HCN laser interferometer for electron density measurements of the JIPP T‐IIU tokamak

Kazuo Kawahata, Kiichiro Haba, Junji Fujita, and Shigeki Okajima

Rev. Sci. Instrum. 60, 3734 (1989); http://dx.doi.org/10.1063/1.1140484 (5 pages) | Cited 12 times

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A six‐channel HCN laser interferometer system has been developed for the measurement of the electron density profile in the JIPP T‐IIU tokamak. The fringe shift of the probe beam is directly read out using a reference beam, the frequency of which is Doppler shifted by 50 kHz with a rotating grating. The optical configuration is of the Michelson interferometer type, of which reflecting mirrors are directly attached on the wall of the vacuum vessel. An effective area of the optical window is only ϕ40 mm. This optical configuration enables us to make the electron density profile measurements by the multichannel laser interferometer with a single small optical window.
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52.70.-m Plasma diagnostic techniques and instrumentation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.55.Fa Tokamaks, spherical tokamaks
07.60.Ly Interferometers

Measurement of the current density profile in the Alcator C tokamak using lithium pellets

E. S. Marmar, J. L. Terry, B. Lipschultz, and J. E. Rice

Rev. Sci. Instrum. 60, 3739 (1989); http://dx.doi.org/10.1063/1.1140485 (5 pages) | Cited 19 times

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High‐speed lithium pellets have been injected into Alcator C tokamak plasmas in order to measure the internal magnetic field, and thus current density profiles. In the pellet ablation cloud, intense visible line radiation from the Li+ ion (λ≊5485 Å, 1s2s 3S−1s2p 3P) is polarized due to the Zeeman effect, and measurement of the polarization angle yields the direction of the total local magnetic field. A ‘‘snap shot’’ of the q profile is obtained as the pellet penetrates from the edge into the center of the discharge, in a time of about 300 μs. The spatial resolution of the measurement is about 1 cm. At a toroidal field of BT=10 T, the emission in the unshifted π component of the Zeeman triplet is more than 80% polarized, and q profiles have been obtained. The pellets are perturbative (〈Δne〉/〈ne〉≊1), but the total pellet penetration time is at least a factor of 1000 smaller than the classical skin time. It can thus be anticipated that the current density profile should not be perturbed significantly during the time of the measurement. With some relatively straightforward modifications and refinements, precision approaching 10% for the measurement of q profiles should be achievable. The technique appears viable, using Li, as long as the toroidal field is ≳4 T.
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52.55.Fa Tokamaks, spherical tokamaks
52.70.Ds Electric and magnetic measurements

Electric probe diagnostics in thermal plasmas: Double probe theory and experimental results

E. Leveroni and E. Pfender

Rev. Sci. Instrum. 60, 3744 (1989); http://dx.doi.org/10.1063/1.1140486 (6 pages) | Cited 13 times

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Electric probes can be advantageously applied to the study of nonequilibrium induced in thermal plasmas by the presence of cold boundaries, since the interpretation of experimental data does not require any assumption about the thermodynamic state of the plasma. An experimental setup and procedure are described which allow accurate measurements of the electron temperature profiles in the near‐wall region of wall stabilized, atmospheric pressure, argon dc arcs. An extension of the classical double floating probe theory was developed to include asymmetries in collecting areas and nonuniformities in the plasma. Excellent agreement between the measured probe characteristics and the analytical relationship was obtained.
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52.70.Nc Particle measurements
52.70.Ds Electric and magnetic measurements
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Space plasma measurements with ion instruments

R. L. Kessel, A. D. Johnstone, A. J. Coates, and R. A. Gowen

Rev. Sci. Instrum. 60, 3750 (1989); http://dx.doi.org/10.1063/1.1141075 (12 pages) | Cited 7 times

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In this article we examine the factors which affect the determination of the plasma bulk parameters in space, with particular emphasis on the density determination. We make this assessment with reference to a particular instrument, the AMPTE‐UKS ion instrument, in order to be specific, but the issues raised here are likely to be encountered in the use of any space plasma instrument containing electrostatic energy analyzers or microchannel plate detectors. We have established a mathematical formalism for determining these parameters by relating the measured counts to the distribution function in terms of the geometric factor. The geometric factor is determined in the calibration of the instrument which is described in some detail. Among the factors we have considered are our calibration techniques, MCP efficiency, detector energy, and angular resolution, as well as the approximations used in our mathematical formalism. To establish confidence in our determination, we used a computer simulation to look for systematic errors in the particular characteristics of the analyzer and to verify the method of extraction of plasma parameters. We can conclude that the detector resolution is adequate for determining density for both solar wind (<5% error) and magnetosheath conditions (<6% error). The detector resolution is also adequate for measuring velocity, <1% error for the solar wind and <3% error in the magnetosheath. The detector resolution is not adequate for determining temperature in the solar wind ∼50%; however, in the magnetosheath where the thermal spread is at least as large as the acceptance angles, the resolution is adequate (<6%). In addition, we tested the influence of the geometric factor on the output bulk parameters by varying the input velocity direction over the entire polar range. The systematic error in the output parameters was less than 5% in all cases.
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52.70.Nc Particle measurements

Small‐signal recovery and analysis with a novel, phase‐locked digital filter

G. T. Gillies, M. B. Scudiere, and S. W. Allison

Rev. Sci. Instrum. 60, 3762 (1989); http://dx.doi.org/10.1063/1.1140487 (7 pages) | Cited 3 times

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A new technique for recovering small signals from large background disturbances is described. The technique combines the narrow‐band sensitivity of synchronous detection via lock‐in amplifier with the waveform‐recovery capabilities of boxcar averaging. However, unlike a boxcar averager, this technique operates in real time. A digital filter‐based realization of this technique phase‐locks to a reference signal at frequencies up to 500 Hz. It samples input at a rate of 256 kHz with 12‐bit precision, recovers the complete synchronous and asynchronous components of the input signal, and reconstructs them with a precision of 12 bits. This allows for either the extraction of or deletion from the original signal of phase‐lockable waveforms. We describe here the design and performance of this instrument and present the results of its use in a signal‐recovery problem made difficult by the presence of power‐line noise.
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84.30.Le Amplifiers
07.05.Hd Data acquisition: hardware and software
07.05.Kf Data analysis: algorithms and implementation; data management
07.05.Rm Data presentation and visualization: algorithms and implementation
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